The Association of Mitochondrial Copy Number With Sarcopenia in Adult Survivors of Childhood Cancer

Associations between mitochondrial copy number, exercise capacity, physiologic cost of walking, and cardiac strain in young adult survivors of childhood cancer

PURPOSE

Childhood cancer survivors are at risk for cardiac dysfunction and impaired physical performance, though underlying cellular mechanisms are not well studied. In this cross-sectional study, we examined the association between peripheral blood mitochondrial DNA copy number (mtDNA-CN, a proxy for mitochondrial function) and markers of performance impairment and cardiac dysfunction.

METHODS

Whole-genome sequencing, validated by quantitative polymerase chain reaction, was used to estimate mtDNA-CN in 1720 adult survivors of childhood cancer (48.5% female; mean age = 30.7 years, standard deviation (SD) = 9.0). Multivariable logistic regression was performed to evaluate the associations between mtDNA-CN and exercise intolerance, walking inefficiency, and abnormal global longitudinal strain (GLS), adjusting for treatment exposures, age, sex, and race and ethnicity.

RESULTS

The prevalence of exercise intolerance, walking inefficiency, and abnormal GLS among survivors was 25.7%, 10.7%, and 31.7%, respectively. Each SD increase of mtDNA-CN was associated with decreased odds of abnormal GLS (adjusted odds ratio (OR) = 0.88, p = 0.04) but was not associated with exercise intolerance (OR = 1.02, p = 0.76) or walking inefficiency (OR = 1.06, p = 0.46). Alkylating agent exposure was associated with increased odds of exercise intolerance (OR = 2.25, p < 0.0001), walking inefficiency (OR = 2.37, p < 0.0001), and abnormal GLS (OR = 1.78, p = 0.0002).

CONCLUSIONS

Increased mtDNA-CN is associated with decreased odds of abnormal cardiac function in childhood cancer survivors.

IMPLICATIONS FOR CANCER SURVIVORS

These findings demonstrate a potential role for mtDNA-CN as a biomarker of early cardiac dysfunction in this population.

Burden of Morbidity and Mortality in Adolescent and Young Adult Cancer Survivors

There are an estimated 650,00 survivors of adolescent and young adult (AYA) cancers in the United States, a number that is expected to markedly increase in the coming decades. The recognition of the potential for some cancer treatments to affect the health of patients for many years after the initial diagnosis has prompted investigators to examine the evolving burden of late morbidity and mortality in AYAs with cancer after treatment completion. Studies in large international cohorts of AYA cancer survivors have now shown that the burden of late effects in survivors treated during the past four decades is substantial, affecting the health and well-being of the survivor, health systems' preparedness to meet their health care needs in the future, and societal economic costs that are largely affected by loss of productivity. We highlight the unique considerations for AYA cancer survivors, identify gaps in knowledge for future research, and provide an overview of emerging efforts to mitigate late effects in these survivors. Ongoing multidisciplinary bench-to-bedside collaborations are critical to understanding the biology of late effects in AYA cancer survivors and to developing personalized interventions to mitigate them. The growing population of AYA cancer survivors makes it imperative that these efforts extend across the cancer care continuum, which will allow survivors to ultimately live to their fullest potential.

Design and methods of a randomized telehealth-based intervention to improve fitness in survivors of childhood cancer with exercise intolerance

BACKGROUND

Exercise intolerance among childhood cancer survivors substantially increases risk for early mortality, reduced cognitive function, poor quality of life, emotional distress, and sub-optimal participation in social roles. Fortunately, exercise intolerance is modifiable, even among individuals with impaired cardiopulmonary and neuromuscular health. This study aims to evaluate the impact of tailored exercise intervention remotely supervised by fitness professionals in survivors with exercise intolerance. Telehealth-based delivery of the intervention aims to enhance uptake by removing the burden of travel and allowing participants to gain confidence with exercise and physical activity at home.

METHODS

This is an ongoing single-blind, two-arm, prospective, clinical trial that will randomize 160 participants 1:1 to intervention (n = 80) and attention control (n = 80) groups. The intervention group receives an individually tailored exercise prescription based on results from baseline assessments performed remotely via a Health Insurance Portability and Accountability Act-compliant virtual platform and personal preferences for aerobic exercise. Each prescription includes aerobic and strengthening components designed to progress gradually to 150-300-min of moderate aerobic activity and twice weekly strengthening exercises over 20-weeks. The first two weeks are supervised for 6 sessions, tapering to twice/week for weeks 3-4, once/week for weeks 5-8, every other week for weeks 9-16 and once midway between weeks 17-20. The schedule is modifiable depending on participant need, adherence, and response to exercise. Each session is approximately one hour.

CONCLUSION

This study tests the efficacy of an individually prescribed, virtually supervised exercise intervention on exercise intolerant childhood cancer survivors.

CLINICALTRIALS

gov registration: NCT04714840.

Frailty and sarcopenia within the earliest national Dutch childhood cancer survivor cohort (DCCSS-LATER): a cross-sectional study

BACKGROUND

Childhood cancer survivors appear to be at increased risk of frailty and sarcopenia, but evidence on the occurrence of and high-risk groups for these aging phenotypes is scarce, especially in European survivors. The aim of this cross-sectional study was to assess the prevalence of and explore risk factors for pre-frailty, frailty, and sarcopenia in a national cohort of Dutch childhood cancer survivors diagnosed between 1963 and 2001.

METHODS

Eligible individuals (alive at the time of study, living in the Netherlands, age 18-45 years, and had not previously declined to participate in a late-effects study) from the Dutch Childhood Cancer Survivor Study (DCCSS-LATER) cohort were invited to take part in this cross-sectional study. We defined pre-frailty and frailty according to modified Fried criteria, and sarcopenia according to the European Working Group on Sarcopenia in Older People 2 definition. Associations between these conditions and demographic and treatment-related as well as endocrine and lifestyle-related factors were estimated with two separate multivariable logistic regression models in survivors with any frailty measurement or complete sarcopenia measurements.

FINDINGS

3996 adult survivors of the DCCSS-LATER cohort were invited to participate in this cross-sectional study. 1993 non-participants were excluded due to lack of response or a decline to participate and 2003 (50·1%) childhood cancer survivors aged 18-45 years were included. 1114 (55·6%) participants had complete frailty measurements and 1472 (73·5%) participants had complete sarcopenia measurements. Mean age at participation was 33·1 years (SD  7·2). 1037 (51·8%) participants were male, 966 (48·2%) were female, and none were transgender. In survivors with complete frailty measurements or complete sarcopenia measurements, the percentage of pre-frailty was 20·3% (95% CI 18·0-22·7), frailty was 7·4% (6·0-9·0), and sarcopenia was 4·4% (3·5-5·6). In the models for pre-frailty, underweight (odds ratio [OR] 3·38 [95% CI 1·92-5·95]) and obesity (OR 1·67 [1·14-2·43]), cranial irradiation (OR 2·07 [1·47-2·93]), total body irradiation (OR 3·17 [1·77-5·70]), cisplatin dose of at least 600 mg/m² (OR 3·75 [1·82-7·74]), growth hormone deficiency (OR 2·25 [1·23-4·09]), hyperthyroidism (OR 3·72 [1·63-8·47]), bone mineral density (Z score ≤-1 and >-2, OR 1·80 [95% CI 1·31-2·47]; Z score ≤-2, OR 3·37 [2·20-5·15]), and folic acid deficiency (OR 1·87 [1·31-2·68]) were considered significant. For frailty, associated factors included age at diagnosis between 10-18 years (OR 1·94 [95% CI 1·19-3·16]), underweight (OR 3·09 [1·42-6·69]), cranial irradiation (OR 2·65 [1·59-4·34]), total body irradiation (OR 3·28 [1·48-7·28]), cisplatin dose of at least 600 mg/m² (OR 3·93 [1·45-10·67]), higher carboplatin doses (per g/m²; OR 1·15 [1·02-1·31]), cyclophosphamide equivalent dose of at least 20 g/m² (OR 3·90 [1·65-9·24]), hyperthyroidism (OR 2·87 [1·06-7·76]), bone mineral density Z score ≤-2 (OR 2·85 [1·54-5·29]), and folic acid deficiency (OR 2·04 [1·20-3·46]). Male sex (OR 4·56 [95%CI 2·26-9·17]), lower BMI (continuous, OR 0·52 [0·45-0·60]), cranial irradiation (OR 3·87 [1·80-8·31]), total body irradiation (OR 4·52 [1·67-12·20]), hypogonadism (OR 3·96 [1·40-11·18]), growth hormone deficiency (OR 4·66 [1·44-15·15]), and vitamin B12 deficiency (OR 6·26 [2·17-1·81]) were significantly associated with sarcopenia.

INTERPRETATION

Our findings show that frailty and sarcopenia occur already at a mean age of 33 years in childhood cancer survivors. Early recognition and interventions for endocrine disorders and dietary deficiencies could be important in minimising the risk of pre-frailty, frailty, and sarcopenia in this population.

FUNDING

Children Cancer-free Foundation, KiKaRoW, Dutch Cancer Society, ODAS Foundation.

Premature aging as an accumulation of deficits in young adult survivors of pediatric cancer

BACKGROUND

We aimed to characterize premature aging as an accumulation of deficits in survivors of pediatric cancer compared with community controls and examine associations with host and treatment factors, neurocognition, and mortality.

METHODS

Pediatric cancer survivors (n = 4000, median age = 28.6, interquartile range [IQR] = 23-35 years; 20 years postdiagnosis: IQR = 15-27), and community participants without a history of cancer serving as controls (n = 638, median age = 32, IQR = 25-40 years) completed clinical assessments and questionnaires and were followed for mortality through April 30, 2020 (mean [SD] follow-up = 7.0 [3.4] years). A deficit accumulation index (DAI) score was calculated from 44 aging-related items including self-reported daily function, psychosocial symptoms, and health conditions. Items were weighted from 0 (absent) to 1 (present and/or most severe), summed and divided by the total yielding a ratio (higher = more deficits). Scores less than 0.20 are robust, and 0.06 is a clinically meaningful difference. Linear regression compared the DAI in survivors and controls with an age*survivor or control interaction. Logistic regression and Cox-proportional hazards estimated the risk of neurocognitive impairment and death. Models were minimally adjusted for age, sex, and race and ethnicity.

RESULTS

The adjusted mean DAI among survivors at age 30 years was 0.16 corresponding to age 63 years in controls (33 years premature aging; β = 0.07, 95% confidence interval [CI] = 0.06 to 0.08; P < .001). Cranial and abdominal radiation, alkylators, platinum, and neurosurgery were associated with worse DAI (P ≤ .001). Higher scores were associated with increased risk of neurocognitive impairment in all domains (P < .001) and increased risk of death (DAI = 0.20-0.35, hazard ratio = 2.80, 95% CI = 1.97 to 3.98; DAI ≥ 0.35, hazard ratio = 5.08, 95% CI = 3.52 to 7.34).

CONCLUSION

Pediatric cancer survivors experience clinically significant premature aging. The DAI may be used to identify survivors at greatest risk of poor health outcomes.

Age-Related Dysfunction in Proteostasis and Cellular Quality Control in the Development of Sarcopenia

Sarcopenia is a debilitating skeletal muscle disease that accelerates in the last decades of life and is characterized by marked deficits in muscle strength, mass, quality, and metabolic health. The multifactorial causes of sarcopenia have proven difficult to treat and involve a complex interplay between environmental factors and intrinsic age-associated changes. It is generally accepted that sarcopenia results in a progressive loss of skeletal muscle function that exceeds the loss of mass, indicating that while loss of muscle mass is important, loss of muscle quality is the primary defect with advanced age. Furthermore, preclinical models have suggested that aged skeletal muscle exhibits defects in cellular quality control such as the degradation of damaged mitochondria. Recent evidence suggests that a dysregulation of proteostasis, an important regulator of cellular quality control, is a significant contributor to the aging-associated declines in muscle quality, function, and mass. Although skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) plays a critical role in cellular control, including skeletal muscle hypertrophy, paradoxically, sustained activation of mTORC1 recapitulates several characteristics of sarcopenia. Pharmaceutical inhibition of mTORC1 as well as caloric restriction significantly improves muscle quality in aged animals, however, the mechanisms controlling cellular proteostasis are not fully known. This information is important for developing effective therapeutic strategies that mitigate or prevent sarcopenia and associated disability. This review identifies recent and historical understanding of the molecular mechanisms of proteostasis driving age-associated muscle loss and suggests potential therapeutic interventions to slow or prevent sarcopenia.

Associations between exercise capacity, p16INK4a expression and inflammation among adult survivors of childhood cancer

BACKGROUND

Over 50% of childhood cancer survivors are exercise intolerant, with maximal aerobic capacities comparable to individuals decades older, suggesting early physiologic ageing. In addition, 36% of survivors are obese. Optimal exercise capacity provides a foundation to support daily function and healthy body habitus and is associated with benefits to cognition, cardiovascular health, and longevity. Cellular senescence and inflammation are key mechanisms that drive age-related disease, quantifiable as biomarkers in peripheral blood.

AIMS

This study aimed to evaluate associations between p16INKa, a biomarker of cellular senescence, and inflammation and exercise capacity among adult survivors of childhood cancer.

MATERIALS AND METHODS

Eligible survivors were recruited from the St. Jude Lifetime (SJLIFE) Cohort Study. Exercise capacity was assessed by maximal oxygen uptake (VO2, ml/kg/min) obtained via cardiopulmonary exercise testing using a modified Bruce protocol. Body fat (%) was determined from dual energy x-ray absorptiometry (DEXA). Peripheral blood samples were used to evaluate log2 p16INK4a mRNA expression, a biomarker of cellular senescence, and inflammation with high sensitivity C-reactive protein (hs-CRP) levels. Multivariable regression evaluated associations between p16INK4a, hs-CRP, body fat, and exercise capacity.

RESULTS

Participants included 185 five-year childhood cancer survivors (mean age 36.6 [range 20.1 - 55.7] years, 44% male, 77% non-Hispanic white, 53% leukemia/lymphoma). Compared to males, females had lower peak VO2 (mean ± SD, 22.5 ± 8.2 vs. 28.8 ± 7.7 ml/kg/min, p<0.01), higher p16INK4a expression (9.6 ± 1.2 vs. 9.2 ± 1.2 fold, p=0.02), and hs-CRP concentration (5.9 ± 8.4 vs. 3.3 ± 3.9 mg/L, p=0.01). Among females (n=103), hs-CRP concentration (β -0.2, 95% CI -0.34 to -0.05, p=0.01) and p16INK4a expression (β-5.32, 95% CI 10.42 to -0.22, p=0.04) were inversely associated and statistically significant with peak exercise capacity, with a significant interaction between p16INK4a expression and body fat (β 0.15, 95% CI 0.02 to 0.28, p=0.03). Among males (n=82), p16INK4a expression (β -1.01, 95% CI -2.14 to 0.12, p=0.08), and body fat (β -0.54, 95% CI -0.70 to -0.38, p<0.01) were inversely associated with peak exercise capacity.

CONCLUSION

Inflammation and p16INK4a expression, a biomarker of cellular senescence, are associated with lower exercise capacity in childhood cancer survivors, suggesting potential targets or outcome measures for interventions designed to prevent or remediate accelerated physiologic ageing in this population.

Endurance exercise attenuates juvenile irradiation-induced skeletal muscle functional decline and mitochondrial stress

BACKGROUND

Radiotherapy is commonly used to treat childhood cancers and can have adverse effects on muscle function, but the underlying mechanisms have yet to be fully elucidated. We hypothesized that endurance exercise following radiation treatment would improve skeletal muscle function.

METHODS

We utilized the Small Animal Radiation Research Platform (SARRP) to irradiate juvenile male mice with a clinically relevant fractionated dose of 3× (every other day over 5 days) 8.2 Gy X-ray irradiation locally from the knee to footpad region of the right hindlimb. Mice were then singly housed for 1 month in cages equipped with either locked or free-spinning voluntary running wheels. Ex vivo muscle contractile function, RT-qPCR analyses, resting cytosolic and sarcoplasmic reticulum (SR) store Ca2+ levels, mitochondrial reactive oxygen species levels (MitoSOX), and immunohistochemical and biochemical analyses of muscle samples were conducted to assess the muscle pathology and the relative therapeutic impact of voluntary wheel running (VWR).

RESULTS

Irradiation reduced fast-twitch extensor digitorum longus (EDL) muscle-specific force by 27% compared to that of non-irradiated mice, while VWR post-irradiation improved muscle-specific force by 37%. Radiation treatment similarly reduced slow-twitch soleus muscle-specific force by 14% compared to that of non-irradiated mice, while VWR post-irradiation improved specific force by 18%. We assessed intracellular Ca2+ regulation, oxidative stress, and mitochondrial homeostasis as potential mechanisms of radiation-induced pathology and exercise-mediated rescue. We found a significant reduction in resting cytosolic Ca2+ concentration following irradiation in sedentary mice. Intriguingly, however, SR Ca2+ store content was increased in myofibers from irradiated mice post-VWR compared to mice that remained sedentary. We observed a 73% elevation in the overall protein oxidization in muscle post-irradiation, while VWR reduced protein nitrosylation by 35% and mitochondrial reactive oxygen species (ROS) production by 50%. Finally, we found that VWR significantly increased the expression of PGC1α at both the transcript and protein levels, consistent with an exercise-dependent increase in mitochondrial biogenesis.

CONCLUSIONS

Juvenile irradiation stunted muscle development, disrupted proper Ca2+ handling, damaged mitochondria, and increased oxidative and nitrosative stress, paralleling significant deficits in muscle force production. Exercise mitigated aberrant Ca2+ handling, mitochondrial homeostasis, and increased oxidative and nitrosative stress in a manner that correlated with improved skeletal muscle function after radiation.